The present invention relates to an air-conditioning installation for motor vehicles, especially for passenger motor vehicles, with a circulation adapted to be switched from cooling to heating of the vehicle interior space by way of a switching device, in which for purposes of cooling the cooling medium flows successively through a compressor, a condenser, an expansion valve, and an evaporator, and in which for purposes of heating the expansion value is by-passed in the opposite flow direction by means of a by-pass line containing a pressure-holding valve.
An air-conditioning system of this type of construction is disclosed in the U.S. Pat. No. DE-OS 30, 47, 955 and features a by-pass line which terminates downstream of the cooling-condenser, respectively, heating-evaporator, in the cooling medium line leading, during heating, at the suction side of the compressor. The cooling-condenser, respectively, heating-evaporator, is therefore not traversed by the flow during heating and thus acts as heat-evaporator only immediately after the beginning of heating for a short period of time until reaching a state of equilibrium.
It is the object of the present invention to further develop the known air-conditioning installation so that the cooling-condenser can be utilized continuously as heating-evaporator during heating in order to enable, in addition to the compression heat of the compressor, a further increased heat output by the heat pump effect, and more particularly at least during the warm-up period of the engine cooling circulation system, up to an engine operating temperature sufficient for the heating purpose and up to a freeze-up of the heating-evaporator which will occur under certain circumstances at an outside temperature near the zero point.
The underlying problems are solved according to the present invention in that the condenser which serves during the heating as heating-evaporator, is of multi-flow or multi-channel construction in a partial section starting from the inlet side during the cooling, or toward the outlet side during heating, and a single channel construction joined to the multi-line construction at a bifurcation joint and wherein the by-pass line terminates in the flow direction during the heating ahead of the bifurcation or within the area of the bifurcation toward the multi-flow or multi-channel area of the heating-evaporator. As a result thereof, the heating-evaporator and the connection thereof to the by-pass line is matched to the evaporation temperature which is particularly low at low temperatures of the cooling medium and to the specific volume of the cooling medium which is very large therewith, so that the evaporation thereof and the flow thereof is favored and the heat output is altogether considerably increased without impairing the function of the cooling-condenser in the counter-flow direction of the cooling medium during the cooling. The cooling medium is thereby also in vapor form during the inflow into the cooling-condenser and thus also has a relatively large specific volume in the first partial area thereof. This single-flow or single-channel partial area of the cooling-condenser which remains in the flow direction during cooling, assures the full cooling output of the air-conditioning installation.
A particularly advantageous division of the cooling-condenser, respectively, heating-evaporator is obtained if the multi-flow or multi-channel partial area amounts to 30% to 50% of the cooling medium volume of the condenser. The temperature-dependent control of the pressure-holding valve which controls the pessure of the cooling fluid in the evaporator, depends on the temperature of the inflowing cooling medium to the pressure holding valve and which within the range of about and below 0.degree. is considerably lower than the pressure at higher temperatures that is controlled to be considerably higher and remains constant. This also takes into consideration the particularly low vapor pressure of the cooling medium at low temperatures with a relatively small cooling medium-feed quantity of the compressor conditioned thereby. In order to assure a rapid start of the heating action of the cooling-evaporator acting as heating-condenser, the pressure value of the pressure-holding valve which is reduced with the temperature of the cooling medium flowing into the same, enables a rapid emptying of the heating-evaporator of cold liquid-cooling medium. At the same time, the vapor-like part of the cooling medium which occurs downstream of the pressure-holding valve as a result of the expansion, limits the pressure decrease on the compressor suction side and assures a sufficiently high cooling medium-density and -feed quantity of the compressor. A particularly advantageous heating function is obtained if the pressure of 15 bar beginning at +5.degree. C. drops to 8 bar at -20.degree. C. According to another feature of the present invention, a time delay switching device is provided which switches the circulatory system during termination of the heating operation with time delay to cooling operation. As a result of this time delay switching action, operating troubles at the end of the heating function by an immediate switching-over of the circulatory system to cooling and therewith possible penetration of liquid cooling medium from the heating-condenser, respectively, cooling-evaporator into the suction side of the compressor are precluded. This is true because up to the point of switching-over, the pressure of the cooling medium is reduced by the cooling off of the cooling medium and a back-flow of the cooling medium fails to take place far-reachingly during a later switching-over. The switching-over device has a normal switch position in its adjustment for heating, thus avoiding the additional structural expenditure of a time-delay switching device and starts with the fact that a heating and cooling one shortly behind the other is not to be expected because of the climatic conditions.
These and other objects, features and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawing which shows, for purposes of illustration only, one embodiment in accordance with the present invention, and wherein: